Stem cells in the embryonic vertebrate olfactory epithelium (OE) generate critical peripheral chemosensory and central neuroendocrine neurons-essential for feeding, social interactions, and reproduction. Nevertheless, mechanisms for establishing and maintaining these embryonic OE stem cells remain unknown. The progeny of embryonic OE stem cells are retained as progenitors throughout life to constantly replace OE chemosensory neurons;however the relationship between embryonic and adult OE stem cells is largely unexplored. We have recently defined apparent stem and transit amplifying cell populations in the embryonic OE. Apparent embryonic OE stem cells express high levels of the transcription factor Meis1 as well as low levels of Sox2, divide slowly and symmetrically, and are necessary for the genesis of olfactory and vomeronasal receptor neurons (ORNs, VRNs) and gonadotropin releasing hormone (GnRH) neurons-the OE neuronal lineage. The apparent transit amplifying cells express neurogenic bHLH genes including Ascl1 as well as high levels of Sox2, undergo rapid terminal neurogenic divisions, and expand numbers of ORNs, VRNs and GnRH neurons. We will now establish transcription regulatory and signaling mechanisms that determine the identity, proliferative capacity, and progression of OE stem or transit amplifying cells through the OE neurogenic lineage. We will determine how embryonic OE stem or transit amplifying cells with distinct transcriptional and signaling histories give rise to precursor populations established in the embryonic OE and retained in the adult to generate ORNs and VRNs throughout life. Specific Aim 1 will define differential influences of transcriptional regulators on OE stem versus transit amplifying cells. Specific Aim 2 will establish molecular mechanisms that underlie a transcription regulatory network essential for OE stem cell identity and lineage progression. Specific Aim 3 will establish the role of local signaling in defining and maintaining a niche for embryonic OE stem cells. Specific Aim 4 will relate the identity of subsets of embryonic OE stem and transit amplifying cells to adult OE progenitor populations. Our experiments therefore provide a mechanistic account of how OE stem cells are established, and how they are regulated to generate ORNs, VRNs and GnRH neurons. The data provide insight into how stem cells in specific niches mediate histogenesis and tissue repair. Our investigation of molecular mechanisms underlying OE stem cell regulation will also identify potential targets for degenerative change associated with diminished olfaction in a number of neurological and psychiatric disorders including Parkinson's and Alzheimer's diseases as well as schizophrenia. PUBLIC HEALTH RELEVANCE: Neural stem cells in the olfactory epithelium (OE) arise in the embryo and are retained throughout life to make neurons that are essential for smell, feeding, social interactions and reproduction. These stem cells may be compromised in several neurodegenerative conditions in which olfactory deficits are early indicators of disease. This project will identify molecular mechanisms that define embryonic OE stem cells, regulate lifelong genesis of olfactory neurons, and are likely pathogenic targets for neurological and psychiatric diseases.